1. Field of the Invention
The present invention relates to an oil-based ink composition for writing instruments and in particular, the present invention relates to the oil-based ink composition for writing instruments that can preferably be used as a gel ink for correction pens that requires no stirring.
2. Description of the Prior Art
Conventionally, oil-based inks for writing instruments that comprise coloring pigments, resins, nonpolar organic solvents, and soluble gelling agents that are soluble to said nonpolar organic solvents have been provided in Patent Document 1 (Japanese Laid-Open Patent Publication 2001-158869). And usually, in gel inks, both storage stability and a leveling property (brush coating and writing performance) of the inks are achieved by increasing static viscosity and decreasing kinematic viscosity.
However, when a single gelling agent is used, usually, said storage stability and said leveling property are in conflicting relationship and so, when one of them shows preference, the other gets worse. In other words, when an ink viscosity is increased by such a soluble gelling agent, the sedimentation of particles of the coloring pigments can be prevented and the storage stability increases, while on the other hand, the leveling property is deteriorated by this effect of increased viscosity upon coating, thereby degrading coating performance and writing performance. On the other hand, when such a soluble gelling agent is used that would set the ink viscosity low, although the leveling property is improved, the storage stability is degraded since the prevention of particle sedimentation of the coloring pigments gets unsatisfactory. As mentioned above, in the oil-based ink for writing instruments that includes coloring pigments, resins, organic solvents, and soluble gelling agents, when a single gelling agent is used, the storage stability and the leveling property of the ink are in trade-off relationship and there used to be a problem of when one is given priority, the other gets worse. From such a view point, conventionally, a single gelling agent was used within such a range that can adjust each of the characteristics.
The object of the present invention is to provide an oil-based ink composition for writing instruments that can further improve the storage stability of the ink while maintaining the leveling property even when said soluble gelling agent is used.